I started designing a CNC router. The bed and beam are supposed to be cast from UHPC (Ultra High Performance Concrete). This is a very dry concrete mix with aggregates that increase its mechanical strength and a plasticiser that makes it viscose enough to be usable for casting again. The end product can achieve mechanical properties comparable to aluminium and has very good vibration dampening properties.

If you’re interested in some of the basic things to consider when designing with concrete, check out this great series on the topic by the “Practical Engineering” channel on youtube.

The design uses 20 mm linear rails all 600 mm long. Ball screws on X and Y are 16 mm SFU and 12 mm SFU on Z. All bearing blocks are standard BK/BF style. Motor flanges are NEMA23. Drawn are JMC iHSV57 servos. The design would also allow to use steppers geared down with pulleys.

Design Notes

The main idea behind the bowl shape is to create a partially enclosed volume that allows to use flood coolant without creating a mess. It also raises the y-rails to an optimal height.

All bearing surfaces are metal pads that are glued into the finished casting and anchored with pins. This allows to achieve high position and alignment accuracy without the need for a large mill. If a mill would be available, milling the bearing surfaces after the glue-up would be ideal.

The port holes in the side are mounts for an optional 4th axis to enable mill turning. They also allow to attach dust extraction when milling wood and double as an all purpose bulkhead.

Two threaded rods put the beam under compression along the x-axis to increase its strength.

This is a fun little 3D print that might be interesting for newcomers to the 3D printing game. The design is based on the mechanical principle of a traditional wooden toy that lets the robot climb up the string if you pull on it.

Parts List

Besides the printed parts you will need an elastic band and a string.I used a elastic band as commonly available for textile work. A normal rubber band might work too but is probably not as long lasting. In any case the band can’t be wider than 5mm (0.19 in) and thicker than 1mm (0.04 in).Not everything will work for the string as the correct amount of friction in the robots “hand” is crucial for the climbing action to work.The model is optimised for a ca. 3mm (0.1 in) or a ca. 2mm string. There are two versions of the clamp available for download. From my experience a coreless braided string works best.

Printing

The model is optimised for printing with a 0.4mm nozzle. The sloped surfaces look best with a 0.2 layer height but larger layer height wont be a problem. Most of the models parts are optimised for printing without support and all are oriented correctly in the STL files for optimal printing. The following parts need extended settings.

STL

support

brim

body-l

x

–

body-r

x

–

arm-l

x

–

arm-r

x

–

head

–

x

Accessories

Assembly

If you printer is tuned to produce precise dimensioned part the robot should friction fit together without glue. Otherwise just use glue or tune up the fit with a file or sanding paper if the parts are too large.

Tuning the clamping mechanism

In general the clamp should clamp just hard enough to hold up the robots own weight. Use a round file to smooth the bottom of the groove the rope runs through in clamp-p1.stl’ to remove all the printing striations. Apart from that it’s important that the hole through the “shoe” is large and smooth enough to let the rope slide through without friction. A good way to achieve this is to bore out the hole with a fitting drill. I chose a 3.5mm drill for the 3mm rope I used.